1. Field of the Invention
The present invention relates to a switch state detection circuit that detects a state of a switch and to a switch system that has the same.
2. Description of Related Art
Conventionally, as disclosed in a patent document 1 (JP-A-2011-70309) and the like, a switch state detection circuit for detecting a state of each switch is proposed. The switch state detection circuit is used together with, for example, a control apparatus (microcomputer or the like), and inform the control apparatus of a detection result of each switch. In this way, the control apparatus can perform control in accordance with the state of each switch.
The switch state detection circuit disclosed in the patent document 1 is provided with detection portions the number of which is equal to or larger than the switches, and each detection portion detects the state of a switch corresponding to the detection portion itself. However, according to such a structure, there is a risk that the number of detection portions increases and a circuit scale of the switch state detection circuit becomes excessively large. This problem becomes more remarkable as a circuit scale of the detection portion becomes especially larger.
Besides, in a case where a plurality of detection portions are included, unevenness occurs in performance among the detection portions, and there is a risk that a suitable detection operation is hampered. Besides, in a case where the state of a switch is detected by using a constant current or the like, if the detection is simultaneously applied to many switches, there is a risk that a total consumed current becomes excessive.